Precambrian

According to scientists who accept the age of the earth as being over 4 billion years, the Precambrian, or Cryptozoic, is the period of the geologic timescale from the formation of Earth (around 4.5 billion years before the present era) to the evolution of abundant macroscopic hard-shelled fossils. This marked the beginning of the Cambrian, some 542 million years ago. These scientists believe that the majority of the evidence existing around the Precambrian has largely been discovered in the past four or five decades. However, they also believe much has been destroyed or hidden by long-term geological processes such as erosion and plate tectonics.